1. Field of the Invention
The invention relates to a skag for a ski. More particularly, the invention relates to a skag that includes dual parallel rails and/or dual parallel keels staggered along the length of the skag, so as to provide improved maneuverability.
2. Description of Related Art
Skis and their use on vehicles are well known. FIG. 1 shows a conventional vehicle 10 (a snowmobile) with a ski 12 thereon. Conventional skis consist of a strip of material that is usually smooth or nearly smooth along its bottom surface. Conventional skis are used to support vehicles or persons on snow, ice, and similar terrain.
It is often desirable to make skis of materials that are relatively light, i.e. to reduce the weight of a vehicle, and/or flexible, i.e. to enable the ski to temporarily flex or deform instead of breaking when it is subjected to stress.
However, the terrain on which skis conventionally are used is often rough, and may subject the skis to considerable wear. Furthermore, even relatively smooth layers of snow, ice, etc. can be highly abrasive under certain conditions. Skis made from many materials that are light and/or flexible may wear out and/or break after a relatively short time.
To address this problem, a more durable material may be attached to the bottom surface of the skis. Sometimes referred to as “rails” or “wear strips”, they are adapted to resist wear, thereby increasing the usable life of the ski. Rails 30A and 30B on conventional skags 20A and 20B can be seen in FIG. 3; a single rail 30 on a conventional skag 20 can also be seen in cross-section in FIG. 4.
In some cases, rather than being disposed directly on the ski, the rail 30 may be disposed on the bottom surface 24 of a carrier platform 22, such as a strip or bar of metal that conforms to and is connected to the bottom surface 14 of the ski 12.
As a further matter, skis without rails or some similar structure have limited ability to “grip” or “bite” snow or ice. This is of special concern when maneuvering the vehicle to which the ski is connected, i.e. when turning. Greater maneuverability may be desirable, especially at high speeds.
The previously described rails 30 or wear strips may provide additional maneuverability beyond that possible with an otherwise smooth ski 12, in addition to increasing durability. By projecting downward into and/or against the snow or ice, the rails 30 provide increased grip, and therefore improved maneuverability.
In addition, it is possible to shape the rail 30 or a portion thereof so as to form a longitudinal keel shape 36, such as a wedge or a blade. Alternatively, a keel 36 can be formed separately and mounted to a ski 12, without necessarily including a rail 30. The keel 36 functions in a manner similar to the rail 30 with regard to maneuverability, i.e. it cuts into the snow, ice, or other terrain on which the ski 12 rests, providing improved bite or grip that enhances performance, stability, and maneuverability.
In common use, the term “skag” sometimes is used to describe such a keel, and sometimes is used to describe a full assembly with such a keel that is attached to a ski. As used herein, the term “skag” is used with the latter definition, that is, a skag is a structure disposed on the lower side of a ski, which includes rails and/or a keel as described above.
A conventional skag typically is attached to the bottom surface 14 of a conventional ski 12. FIG. 2 shows a pair of conventional skis 12A and 12B with conventional skags 20A and 20B on their bottom surfaces 14A and 14B. FIGS. 2 and 3 show a pair of conventional skags 20A and 20B in greater detail, and a cross-section of a single conventional skag 20, respectively.
Conventional skags have several limitations.
First, because it cuts into the underlying surface, the keel 36 of a conventional skag 20 often leaves behind a trail or groove. If a second vehicle with a conventional skag 20 later follows the same path, the skag 20 on that second vehicle may follow the track from the first vehicle, thereby aligning the second vehicle's ski with the path followed by the first vehicle. Later vehicles also may follow the track, making it deeper and more pronounced.
As a result, the second and later vehicles tend to follow closely the path of the first vehicle, and resist efforts to steer out of that path. In addition, the second and later vehicles tend to shift, sometimes abruptly, to align themselves with the path of the first vehicle if that path is crossed. These phenomena are sometimes collectively referred to as “groove follow”. The former also may be referred to as “tracking”, while the latter may be referred to as “darting”. Both phenomena may affect the maneuverability of the second and later vehicles.
Although it is possible to overcome darting and tracking by deliberately steering a vehicle out of the path of preceding vehicles, or by avoiding such earlier paths altogether, such solutions may not always be desirable.
For example, snowmobiles, which have used skis with conventional skags, are often used on dedicated snowmobile trails. Trails are not always sufficiently spacious to make it possible for vehicle operators to avoid the grooves left by previous vehicles. This is especially true in popular trails, and in areas of heavy traffic on a trail.
Furthermore, even if it is possible to make a special effort to avoid grooves from previous vehicles, it may be difficult or undesirable to do so.
Attempts to overcome this problem have been made. For example, in U.S. Pat. No. 5,344,168 to Olson et al., a generally flat bar is employed to disrupt existing skag grooves in an effort to avoid tracking and darting. However, the addition of this bar increases the drag on the ski, since in order for the bar to function it must dig into and break up the snow or ice in order to fill in the groove. Furthermore, the bar may not be effective in disrupting grooves in hard packed snow, or in wet snow that has frozen into ice.
Another feature of conventional skags that might be improved is the ability to maneuver. Although conventional skags provide increased maneuverability over skis lacking such structures, still greater maneuverability may be desired, especially at high speeds.
The ability to maneuver with a ski with a skag thereon depends in part upon the size of the skag's rail and/or keel. As the skag is made longer, it provides greater grip or “bite” into the underlying surface, thereby allowing more force to be applied when turning.
In addition, increasing the length of a skag reduces the total weight per unit length that must be borne thereby, assuming vehicle weight is not also increased when the skag is lengthened. This may contribute to reduced wear on the skag.
However, a long longitudinal skag also has disadvantages. For example, although the skag provides maneuverability, the skag itself must be made to turn against the snow or ice surrounding it on both sides. Thus, as the skag is lengthened, more force is required to turn it.
Furthermore, a ski on a vehicle that is turning typically follows a curved path. As the length of a conventional straight skag increases, the ends of the skag deviate by a greater distance from that curved path. A long straight skag following a curved path may cause the vehicle to turn roughly, or in “stutters”.
Also, turning a ski with a skag thereon puts stress on the skag. As the skag length increases, the stress increases. At some point this can contribute to greater wear, and/or damage to the skag as a whole, its component parts, and/or the ski to which it is attached. For example, the increased stresses experienced by long skags may cause the skag to eventually become worn to the point that it must be replaced. The increased stresses for a long ski skag may also result in the failure of the ski skag, i.e. by the keel separating from the rail, by the rail separating from the carrier platform, by the skag or some portion thereof bending into an S-curve or otherwise deforming, etc. Because stress increases with increasing skag length, a longer ski skag is proportionally weaker than a shorter one, assuming they are made from similar materials using similar methods of construction.
Thus, although it is in some respects desirable to increase the total length of the skag, other factors limit the utility and durability of long conventional skag. For this reason, increasing the length of a conventional skag beyond a certain point does not provide further improvements in maneuverability for a vehicle equipped with a conventional skag.
Another limitation of conventional skags is that they may not be at full effectiveness in tight turns. When a vehicle turns, its skis typically do not lay flat on the underlying surface, but rather tilt into the turn. Under such conditions, the area of contact between the ski and the surface moves towards the edge of the ski, in the direction of the turn. The tighter the turn, the greater the tilt, and the more extreme the shift in contact area.
Skags are conventionally disposed in the center of a ski. As the ski comes to rest more on its edge, conventional skags are lifted at least partially out of contact with the underlying surface. As the skags lose contact with the surface, the ability of the skag to affect the maneuverability of the vehicle decreases. A skag that is shifted to one edge of a ski may compensate at least partially, but only for turns in one direction, and it may aggravate it when turning in the opposite direction.
A skag may incorporate multiple rails and/or keels. A patent application entitled DUAL SKI SKAG was filed on such an arrangement on Feb. 18, 2003. The serial number for that application is not available as of the filing date of the present application.
Such an arrangement is illustrated in FIG. 5. Therein, a pair of skags 220A and 220B are shown. Skag 220A has rails 230A and 240A, and skag 220B has rails 230B and 240B. Keels 236A, 246A, 236B, and 246B are disposed on rails 230A, 240A, 230B, and 240B respectively.
A dual skag arrangement as illustrated in FIG. 5 may increase the total effective length of the skag without necessarily increasing its actual length. However, the use of dual skags 220A and 220B also has limitations.
For example, the weight of a dual skag may be increased by the addition of a second rail and/or keel. This is of special concern when such a skag is used for vehicles intended for high speed and/or high acceleration, such as racing snowmobiles.
In addition, the increased quantities of material necessary to produce a dual skag may increase its cost. In particular, hard, durable materials suitable for use as keels, such as carbides, may be relatively expensive. Furthermore, producing a dual skag may increase the costs for manufacturing the skag, the time required, etc.
A dual skag also may be prone to a phenomenon sometimes referred to as “pop-up”. Each of the rails 230A, 240A, 230B, and 240B and the keels 236A, 246A, 236B, and 246B shown in FIG. 5 has some width. Although neither FIG. 5 nor the other figures herein are necessarily to scale, it will be appreciated from FIG. 5 that some volume of snow or other material may be displaced by the rails 230A, 240A, 230B, and 240B and/or the keels 236A, 246A, 236B, and 246B. Under certain conditions, some of the displaced snow is forced into the space between each pair of adjacent rails. This may have the effect of forming a raised ridge of snow centered between adjacent rails.
The creation of this ridge of snow may be sufficient to cause the ski to pop upwards out of contact with the surrounding snow. Consequently, the full advantage of the skag may not be obtained. The sudden motion of repeated pop-ups may contribute to increased wear on the skag, the ski, or other components of the vehicle. In addition, pop-up may produce noise and/or vibration.
Pop up is of special concern in relatively light vehicles, since their lower weight means they can be lifted more easily from the surface of the snow if and when such ridges form.
As an additional matter, producing ridges sufficient to cause a vehicle's ski to pop up may not be desirable in itself, insofar as maintaining good trail conditions, etc.
As noted previously, in a conventional skag with a keel thereon, the keel typically does not run the full length of the rail. Certain performance drawbacks of very long keels are described above. In addition, although it may be advantageous to construct keels of extremely hard materials, such materials can be relatively expensive to obtain, and may require considerable labor and/or special equipment to produce and install. Consequently, in conventional skags a significant portion of the rails are not covered by keels, and thus are not protected from wear by the keels.
As a result, the portions of the rail that are not protected by the keel may wear more quickly than the portions that are. This may be especially true for vehicles that travel at high speeds, operate on hard or rough surfaces such as ice or frozen snow, etc.